Phospholipid exchange proteins catalyze the translocation of intact phospholipid molecules between membranes. The major phospholipid exchange protein from bovine cerebral cortex exhibits specificity for phosphatidylinositol and phosphatidylcholine. A critical step in the catalytic process is the formation of a transient complex between the exchange protein and membrane surface, during which time protein-bound and membrane-bound phospholipids are exchanged. This research program will continue the detailed investigation of membrane-phospholipid exchange protein interactions as well as phospholipid-phospholipid exchange protein interactions. One series of experiments involves the chemical modification of selected amino acyl residues and the subsequent effects on phospholipid binding, membrane interaction, and catalytic activity; additional information about the phospholipid binding domain derives from protein-bound photosensitive and fluorescent phospholipids. A second series of experiments concerns the spectroscopic analysis of these events, using circular dichroism and intrinsic fluorescence of the delipidated protein, tha phospholipid-protein complex, and the membrane-protein complex; these studies also measure the intensity, quenching, polarization, and lifetime of various fluorescent probes, both protein-bound and membrane-bound. A third series of experiments deals with perturbations of the phospholipid bilayer and the effects on phospholipid exchange activity, perturbations induced by local anesthetics and lateral phase separations. The common thread throughout this program is the physicochemical basis of lipid-protein interactions at (1) the substrate level with individual phospholipid molecules and (2) the surface level with phospholipid bilayer membranes. The information obtained will help to define the biological roles of phospholipid exchange proteins in phosphatidylinositol metabolism and membrane and biogenesis and homeostasis.